Generally, ultra-fine particles are manufactured by a method of collecting them through a filter or sticking them to a collecting plate after they have been formed by using flames or a furnace. According to this method, metal oxides such as SiO2 or Fe2O3 having ultrahigh purity are obtained.
However, in conventional methods for manufacturing the ultra-fine particles, there are some disadvantages in that their collecting efficiency is very low, and in that sizes of the collected ultra-fine particles cannot be controlled. In addition, there are problems in that most of the ultra-fine particles that are not collected cannot be recovered, and in that since the ultra-fine particles that have not been recovered are mainly metal oxides, they may contaminate the environment. Especially, in the conventional methods for manufacturing the ultra-fine particles by using the filter, there is a trouble in that the filter should be frequently replaced due to serious contamination of the filter.
The study of the electro-hydrodynamic atomization(EHDA) or electrospraying has been carried out for a long time. In addition, the formation of electrically charged fine liquid droplets has been actively studied in recent years since a variety of industrial fields are very interested in the use of such liquid droplets. Electro-hydrodynamic atomizer have been preferably used for producing highly charged fine liquid droplets. Such atomizer form desired highly charged fine liquid droplets by exposing the droplets to an electric field having a high voltage difference. An example of such an electro-hydrodynamic atomizer is disclosed in U.S. Pat. No. 5,873,523. In addition, another example of the electro-hydrodynamic atomizer is described in detail in the specification and drawings of Korean Patent Application No. 2000-4208 (not laid-open), which is also owned by the applicant of the present application.
Liquid droplets generated from the electro-hydrodynamic atomizer are extremely small in the order of several ten nanometers and are highly charged. Such highly charged liquid droplets are used as an ion source or the like of a mass spectrometer.